Pneumatic Tire

ABSTRACT

In a pneumatic tire, bead cores have a wire arrangement. In a cross-sectional view in a tire meridian direction, a tangential line and a contact point are defined. The tangential line contacts an innermost layer in a radial direction and the wire cross sections innermost and outermost in a lateral direction in the wire arrangement from a rim fitting surface side. The contact point of the tangent line is on the wire cross section on the outermost side. A gauge Wh in the lateral direction from the contact point to the rim fitting surface and an outer diameter φ of the bead wire have a relationship 2.0≤Wh/φ≤15.0. A radial height H2 of a contact portion between a body portion and a turned back portion of a carcass layer has a relationship 0.80≤H2/H1≤3.00 to a radial height H1 of the bead cores.

TECHNICAL FIELD

The technology relates to a pneumatic tire and particularly relates to apneumatic tire that can improve durability of the tire while a weight ofthe tire is reduced.

BACKGROUND ART

In recent years, for weight reduction of a tire, weight reduction ofbead portions has been advanced. As a conventional pneumatic tire, atechnology described in Japan Unexamined Patent Publication No.2008-149778 has been known. In Japan Unexamined Patent Publication No.2008-149778, bead fillers are omitted to reduce a weight of the tire.

However, in the conventional pneumatic tire described above,deterioration of durability of the tire due to the omission of the beadfillers is a concern.

SUMMARY

The technology provides a pneumatic tire that can improve durability ofthe tire while a weight of the tire is reduced.

A pneumatic tire according to an embodiment of the technology includesbead cores, a carcass layer, and a rim cushion rubber. The bead coresare formed by annularly and multiply winding one or a plurality of beadwires. The carcass layer is formed of a carcass ply of a single layer ora plurality of layers. The carcass layer is turned back so as to wrapthe bead cores and extended between the bead cores. The rim cushionrubber is disposed along a turned back portion of the carcass layer toconstitute a rim fitting surface of a bead portion. The turned backportion of the carcass layer contacts a body portion of the carcasslayer in a cross-sectional view in a tire meridian direction to form aclosed region surrounding the bead cores. A rubber occupancy ratio inthe closed region is in a range of 15% or less. The bead cores have apredetermined wire arrangement structure formed by arranging wire crosssections of the bead wires in the cross-sectional view in the tiremeridian direction. A tangential line L1 and a contact point C2 aredefined. The tangential line L1 contacts an innermost layer in a tireradial direction and the wire cross sections innermost and outermost ina tire lateral direction in the wire arrangement structure from the rimfitting surface side. The contact point C2 of the tangent line L1 is onthe wire cross section on the outermost side. A gauge Wh in the tirelateral direction from the contact point C2 to the rim fitting surfaceand an outer diameter φ of the bead wire have a relationship2.0≤Wh/φ≤15.0. A radial height H2 of a contact portion between the bodyportion and the turned back portion of the carcass layer has arelationship 0.80≤H2/H1≤3.00 to a radial height H1 of the bead cores.

In the pneumatic tire according to an embodiment of the technology, (1)the rubber occupancy ratio in the closed region X surrounded by the bodyportion and the turned back portion of the carcass layer is set to beconsiderably low, and therefore there is an advantage that a weight ofthe tire can be reduced. Additionally, (2) the ratio Wh/φ brings anadvantage that the gauge Wh of the rim fitting portion is madeappropriate, and (3) the range of the ratio H2/H1 brings an advantagethat the radial height H2 of the self-contact portion of the carcasslayer is made appropriate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of thetechnology.

FIG. 2 is a cross-sectional view illustrating a bead portion of thepneumatic tire illustrated in FIG. 1.

FIG. 3 is an enlarged view illustrating a rim fitting portion of thebead portion illustrated in FIG. 2.

FIG. 4 is an explanatory diagram illustrating a wire arrangementstructure of bead cores illustrated in FIG. 3.

FIG. 5 is an explanatory diagram illustrating the rim fitting portion ofthe bead portion in a state where the tire is mounted on a rim.

FIG. 6 is an explanatory diagram illustrating the rim fitting portionillustrated in FIG. 3.

FIG. 7 is an explanatory diagram illustrating the rim fitting portionillustrated in FIG. 3.

FIG. 8 is an explanatory diagram illustrating a modified example of thebead cores illustrated in FIG. 4.

FIG. 9 is an explanatory diagram illustrating a modified example of thebead cores illustrated in FIG. 4.

FIG. 10 is an explanatory diagram illustrating a modified example of thebead cores illustrated in FIG. 4.

FIG. 11 is an explanatory diagram illustrating a modified example of thebead cores illustrated in FIG. 4.

FIG. 12 is an explanatory diagram illustrating a modified example of thebead cores illustrated in FIG. 4.

FIG. 13 is an enlarged view illustrating a tire side portion of thepneumatic tire illustrated in FIG. 1.

FIG. 14 is a table showing results of performance tests of pneumatictires according to embodiments of the technology.

FIG. 15 is an explanatory diagram illustrating bead cores of a test tireof Conventional Example.

DETAILED DESCRIPTION

Embodiments of the technology are described in detail below withreference to the drawings. However, the technology is not limited tothese embodiments. Moreover, constituents of the embodiments includeelements that are substitutable while maintaining consistency with thetechnology, and obviously substitutable elements. Furthermore, themodified examples described in the embodiments can be combined asdesired within the scope apparent to one skilled in the art.

Pneumatic Tire

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of thetechnology. The same drawing illustrates a cross-sectional view of ahalf region in the tire radial direction. Also, the same drawingillustrates a radial tire for a passenger vehicle as an example of apneumatic tire.

In reference to the same drawing, “cross section in a tire meridiandirection” refers to a cross section of the tire taken along a planethat includes the tire rotation axis (not illustrated). Reference signCL denotes the tire equatorial plane and refers to a plane normal to thetire rotation axis that passes through the center point of the tire inthe tire rotation axis direction. “Tire lateral direction” refers to thedirection parallel with the tire rotation axis. “Tire radial direction”refers to the direction perpendicular to the tire rotation axis.

A pneumatic tire 1 has an annular structure with the tire rotation axisas its center and includes a pair of bead cores 11, 11, a carcass layer13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16,16, a pair of rim cushion rubbers 17, 17, and an innerliner 18 (see FIG.1).

The pair of bead cores 11, 11 are formed by annularly and multiplywinding one or a plurality of bead wires made of steel. The pair of beadcores 11, 11 are embedded in bead portions to constitute cores of theright and left bead portions.

The carcass layer 13 has a single layer structure formed of one carcassply or a multilayer structure formed by layering a plurality of carcassplies, and extends between the right and left bead cores 11, 11 in atoroidal shape, forming the framework of the tire. Additionally, bothend portions of the carcass layer 13 are turned back outwardly in thetire lateral direction so as to wrap around the bead cores 11 and fixed.The carcass ply (plies) of the carcass layer 13 is made by performing arolling process on a plurality of coating rubber-covered carcass cordsmade of steel or an organic fiber material (e.g., aramid, nylon,polyester, and rayon). The carcass ply (plies) has a carcass angle(defined as an inclination angle of a longitudinal direction of thecarcass cords with respect to the tire circumferential direction), as anabsolute value, ranging from 80 degrees or greater to 90 degrees orless. Although the configuration of FIG. 1 has the single layerstructure in which the carcass layer 13 is formed of the single carcassply, no such limitation is intended, and the carcass layer 13 may have amultilayer structure formed by layering the plurality of carcass plies.

The belt layer 14 is formed by layering a pair of cross belts 141, 142,a belt cover 143, and a pair of belt edge covers 144, and arranged to bewound around the periphery of the carcass layer 13. The pair of crossbelts 141, 142 are made by performing a rolling process on a pluralityof coating rubber-covered belt cords made of steel or an organic fibermaterial. The cross belts 141, 142 have a belt angle, as an absolutevalue, ranging from 20 degrees or greater to 55 degrees or less. Notethat the belt angles of the cross belts 141, 142 are not limited to therange described above, and any angle can be set. Furthermore, the pairof cross belts 141, 142 have belt angles (defined as inclination anglesof the longitudinal direction of the belt cords with respect to the tirecircumferential direction) of mutually different signs, and the crossbelts 141, 142 are layered so that the longitudinal directions of thebelt cords intersect with one another (so-called crossply structure).The belt cover 143 and the pair of belt edge covers 144 are made bycoating belt cover cords made of steel or an organic fiber material witha coating rubber and have belt angles, as an absolute value, from 0degrees or greater to 10 degrees or less. Further, the belt cover 143and the pair of belt edge covers 144 are, for example, a strip materialformed by coating one or a plurality of belt cover cords with a coatingrubber and winding the strip material spirally around the outercircumferential surfaces of the cross belts 141, 142 multiple times inthe tire circumferential direction. Note that the belt cover 143 and thepair of belt edge covers 144 may be omitted (not illustrated).

The tread rubber 15 is disposed outward of the carcass layer 13 and thebelt layer 14 in the tire radial direction and constitutes a treadportion of the tire. The pair of sidewall rubbers 16, 16 are disposedoutward of the carcass layer 13 in the tire lateral direction andconstitute right and left sidewall portions. The pair of respective rimcushion rubbers 17, 17 are disposed inward of the right and left beadcores 11, 11 and the turned back portions of the carcass layer 13 in thetire radial direction to constitute rim fitting surfaces of the beadportions.

The innerliner 18 is an air penetration preventing layer that isdisposed on the tire cavity surface and covers the carcass layer 13. Theinnerliner 18 also suppresses oxidation caused by exposure of thecarcass layer 13 and prevents air inside the tire from leaking. Inaddition, the innerliner 18 is constituted by, for example, a rubbercomposition with butyl rubber as a main component, thermoplastic resin,thermoplastic elastomer composition made by blending an elastomercomponent with a thermoplastic resin, and the like. The innerliner 18 isadhered to the carcass layer 13 via a tie rubber (not illustrated).

Bead Filler-Less Structure

FIG. 2 is a cross-sectional view illustrating the bead portion of thepneumatic tire illustrated in FIG. 1. The same drawing illustrates across-sectional view in the tire meridian direction of the bead portionin a state before mounting of the tire on a rim.

As illustrated in FIG. 2, the carcass layer 13 is turned back outwardlyin the tire lateral direction so as to wrap around the bead cores 11 andfixed. At this time, a closed region X surrounding the bead cores 11 isformed by contact of a turned back portion 132 of the carcass layer 13with a body portion 131. Also, the closed region X continuous across theentire circumference of the tire forms an annular closed spacesurrounding the bead cores 11.

The closed region X is defined as a region surrounded by the carcass plyof the carcass layer 13 in a cross-sectional view in the tire meridiandirection. Specifically, the area surrounded by the surface of the coatrubber of the carcass ply is defined as the closed region X.

Also, in the configuration of FIG. 2, the carcass layer 13 is formed ofthe single-layer carcass ply, and the closed region X is formed byself-contact of the carcass ply. On the other hand, in a configurationin which the carcass layer 13 is formed of the plurality of layeredcarcass plies (not illustrated), the closed region X can be formed bymutual contact of the different carcass plies. For example, thefollowing configuration (not illustrated) is assumed. The carcass layer13 has a two-layer structure formed by layering first and second carcassplies, a turned back portion of the first carcass ply terminates in themiddle of a radial height H1 (see FIG. 2) of the bead cores 11 withoutin contact with the body portion, and a turned back portion of thesecond carcass ply extends to radially outward of the bead cores 11 andis in contact with the body portion of the first carcass ply.

At this time, a rubber occupancy ratio in the closed region X ispreferably in the range of 15% or less, more preferably in the range of10% or less, and further preferably in the range of 5% or less.Accordingly, the rubber occupancy ratio in the closed region Xsurrounded by the body portion 131 and the turned back portion 132 ofthe carcass layer 13, that is, a rubber volume around the bead cores 11,is set to be considerably low. Thus, a purpose of reducing the weight ofthe tire brought by omission of bead fillers is achieved. Note that thelower limit of the rubber occupancy ratio is not particularly limitedbut is preferably 0.1% or higher. Thus, an amount of insulation rubberof the bead cores 11 is properly ensured.

The rubber occupancy ratio is calculated as a proportion (%) of across-sectional area of the rubber materials in the closed region X tothe overall cross-sectional area of the closed region X in thecross-sectional view in the tire meridian direction.

For example, in the configuration of FIG. 2, the turned back portion 132of the carcass layer 13 is turned back without including a bead fillerin the closed region X and in contact with the body portion 131. Also,the carcass ply of the carcass layer 13 is wound up along the outercircumferential surfaces of the bead cores 11. Thus, only constituentmembers of the bead cores 11 are present in the closed area X. Theconstituent members of the bead cores 11 include bead wires 111, theinsulation rubbers, bead covers, and wrapping threads.

Note that the bead filler is a reinforcing rubber disposed so as to fillthe triangular gap between the bead cores, the body portion, and theturned back portion of the carcass layer, and is disposed to increaserigidity of the bead portion. The bead filler generally has a triangularcross section and has a rubber hardness from 65 or greater to 99 orless.

The rubber hardness is measured in accordance with JIS (JapaneseIndustrial Standard) K 6253.

Additionally, in the above-described configuration in which the beadfiller is omitted, as illustrated in FIG. 2, the turned back portion 132of the carcass layer 13 is preferably in surface contact with the bodyportion 131 of the carcass layer 13 and fixed. Additionally, a radialheight H2 of the contact portion between the body portion 131 and theturned back portion 132 of the carcass layer 13 preferably has arelationship 0.80≤H2/H1≤3.00 to the radial height H1 of the bead cores11, and more preferably has a relationship 1.20≤H2/H1≤2.50. Thus, theradial height H2 of the self-contact portion of the carcass layer 13 ismade appropriate. In other words, the lower limit causes the turned backportion 132 to stably contact the body portion 131, thus improvingdurability of the bead portion. In addition, the upper limit suppressesan increase in tire weight due to the excessive amount of the turnedback portion 132.

The radial height H1 of the bead cores is measured as the maximum heightin the tire radial direction from the innermost layer in the wirearrangement structure of the bead cores in the tire radial direction andthe inner end in the tire radial direction of the wire cross sectionoutermost in the tire lateral direction to an outermost layer in thetire radial direction and an outer end in the tire radial direction ofthe wire cross section outermost in the tire lateral direction.

The radial height H2 of the self-contact portion of the carcass layer ismeasured as the maximum length of the contact portion between the bodyportion and the turned back portion of the carcass layer in the tireradial direction.

Additionally, as illustrated in FIG. 2, in the configuration describedabove, an end portion (reference sign is omitted in the drawing) of theturned back portion 132 of the carcass layer 13 preferably contacts thebody portion 131 of the carcass layer 13. In such a configuration,stress concentration at the end portion of the turned back portion 132is reduced compared to a configuration in which the end portion of theturned back portion 132 is spaced apart from the body portion 131 (notillustrated). Accordingly, separation of the peripheral rubber startingfrom the end portion of the turned back portion 132 is suppressed.

Additionally, an actual length La2 (dimension symbol is omitted in thedrawing) of the contact portion between the body portion 131 and theturned back portion 132 of the carcass layer 13 preferably has arelationship 0.30≤La2/La1≤2.00 to a circumferential length La1(dimension symbol is omitted in the drawing) of the closed region X, andmore preferably has a relationship 0.37≤La2/La1≤1.80. Thus, the actuallength La2 of the self-contact portion of the carcass layer 13 is madeappropriate. That is, the lower limit properly ensures springcharacteristics of the carcass layer 13, ensures steering stability ondry road surfaces, and ensures the durability of the bead portion. Inaddition, the upper limit suppresses an increase in tire weight due tothe excessive amount of the turned back portion 132.

The circumferential length La1 of the closed region X is measured as aperiphery length of the surface of the carcass ply constituting theboundary line of the closed region X in the cross-sectional view in thetire meridian direction.

The actual length La2 of the contact portion is measured as a peripherylength at the self-contact portion between the body portion and theturned back portion of the carcass layer in the cross-sectional view inthe tire meridian direction.

Outer Side Reinforcing Rubber

As illustrated in FIG. 2, the pneumatic tire 1 includes an outer sidereinforcing rubber 19, in addition to the sidewall rubber 16 and the rimcushion rubber 17 described above.

Each of the sidewall rubbers 16 are disposed outward of the carcasslayer 13 in the tire lateral direction and constitute the sidewallportions of the tire as described above. Additionally, the rubberhardness of the sidewall rubber 16 is in the range from 40 or greater to70 or less. Furthermore, elongation at break of the sidewall rubber 16is in the range from 400% or greater to 650% or less.

The elongation at break is measured in accordance with the JIS K6251standard.

The rim cushion rubber 17 is disposed inward of the bead cores 11 andthe turned back portion 132 of the carcass layer 13 in the tire radialdirection to constitute the rim fitting surface of the bead portion asdescribed above. Additionally, the rubber hardness of the rim cushionrubber 17 is in the range from 50 or greater to 80 or less. Furthermore,the elongation at break of the rim cushion rubber 17 is in the rangefrom 150% or greater to 450% or less.

The outer side reinforcing rubber 19 is disposed to be sandwichedbetween the turned back portion 132 of the carcass layer 13 and the rimcushion rubber 17 (see FIG. 2). In such a configuration, particularly inthe configuration in which the bead filler is omitted described above,the spring characteristics of the bead portion are reinforced by theouter side reinforcing rubber 19, the steering stability on dry roadsurfaces is ensured, and the durability of the bead portion is improved.

Furthermore, the rubber hardness of the outer side reinforcing rubber 19is preferably in the range from 65 or greater to 105 or less, and morepreferably in the range from 70 or greater to 100 or less. Thus, theabove effect of the outer side reinforcing rubber 19 is properlyensured.

Additionally, the rubber hardness of the outer side reinforcing rubber19 is higher than the rubber hardnesses of the sidewall rubber 16 andthe rim cushion rubber 17. Specifically, a difference ΔHs_SW between therubber hardness of the sidewall rubber 16 and the rubber hardness of theouter side reinforcing rubber 19 is preferably seven or greater, andmore preferably 12 or greater. Additionally, a difference ΔHs_RC betweenthe rubber hardness of the rim cushion rubber 17 and the rubber hardnessof the outer side reinforcing rubber 19 is preferably three or greater,and more preferably seven or greater. Accordingly, the reinforcingeffect of the spring characteristics of the bead portion caused by theouter side reinforcing rubber 19 is appropriately exhibited. Note thatthe lower limit of the difference ΔHs_SW in rubber hardness is subjectto restrictions by the lower limit of the rubber hardness of the outerside reinforcing rubber 19 described above.

Furthermore, the elongation at break of the outer side reinforcingrubber 19 is preferably in the range from 50% or greater to 400% orless, and more preferably in the range from 70% or greater to 350% orless.

For example, in the configuration of FIG. 2, the rim cushion rubber 17extends over completely from a bead toe Bt to a bead base Bb to form therim fitting surface to a bead sheet 101 of a rim 10. Additionally, therim cushion rubber 17 extends outward in the tire radial direction fromthe bead base Bb along the turned back portion 132 of the carcass layer13 to form a fitting surface to a flange 102 of the rim 10.Additionally, an end portion outward of the rim cushion rubber 17 in thetire radial direction is inserted between the carcass layer 13 and thesidewall rubber 16, and extends outward in the tire radial directionwith respect to the end portion of the turned back portion 132 of thecarcass layer 13 and the flange 102 of the rim 10. Additionally, thebead portion may include a chafer (not illustrated).

Note that the rim cushion rubber 17 preferably extends to at least aregion from a bead heel Bh to a center portion (a midpoint Cm describedlater) of an innermost layer in the tire radial direction of the beadcores 11. Thus, the durability of the rim fitting portion of the beadportion is properly secured.

Additionally, in the configuration of FIG. 2, the outer side reinforcingrubber 19 has a shape long in the tire radial direction, and issandwiched between the turned back portion 132 of the carcass layer 13and the rim cushion rubber 17. Additionally, the end portion inward inthe tire radial direction of the outer side reinforcing rubber 19overlaps with the bead core 11 in the tire radial direction.Additionally, the outer side reinforcing rubber 19 extends outward inthe tire radial direction with respect to the end portion of the turnedback portion 132 of the carcass layer 13, and is sandwiched between thebody portion 131 of the carcass layer 13 and the sidewall rubber 16.Additionally, the outer side reinforcing rubber 19 covers the endportion of the turned back portion 132 of the carcass layer 13 fromoutward in the tire lateral direction. Additionally, the outer sidereinforcing rubber 19 is adjacent to the turned back portion 132 of thecarcass layer 13 over the entire contact portion between the bodyportion 131 and the turned back portion 132 of the carcass layer 13.Thus, the spring characteristics of the bead portion are appropriatelyreinforced by the outer side reinforcing rubber 19, the steeringstability on dry road surfaces is improved, and the durability of thebead portion is improved. Additionally, the rubber hardness of the outerside reinforcing rubber 19 is higher than the rubber hardnesses of thesidewall rubber 16 and the rim cushion rubber 17. Accordingly, adistribution of the rubber hardness at or near the end portion of theturned back portion 132 of the carcass layer 13 decreases from the endportion of the carcass layer 13 toward the surface of the tire sideportion. Accordingly, stress generated at or near the end portion of thecarcass layer 13 is reduced, and separation of the peripheral rubber issuppressed.

Additionally, a radial height H3 from a measurement point of a tireinner diameter RD to an end portion outward of the outer sidereinforcing rubber 19 in the tire radial direction and a tirecross-sectional height SH (see FIG. 1) preferably have a relationship0.10≤H3/SH≤0.60, and more preferably have a relationship0.15≤H3/SH≤0.50. Accordingly, the radial height H3 of the outer sidereinforcing rubber 19 is made appropriate. In other words, the lowerlimit appropriately reinforces the spring characteristics of the beadportion by the outer side reinforcing rubber 19, improves the steeringstability on dry road surfaces, and improves the durability of the beadportion. In addition, the upper limit suppresses an increase in tireweight due to the excessive amount of the outer side reinforcing rubber19.

The tire inner diameter RD is equal to a rim diameter of a specifiedrim.

The radial height H3 is measured when the tire is mounted on thespecified rim, inflated to a specified internal pressure, and in anunloaded state. Specifically, the radial height H3 is calculated as adifference between the diameter of the end portion outward of the outerside reinforcing rubber 19 in the tire radial direction and the tireinner diameter RD.

The tire cross-sectional height SH is a distance half of the differencebetween the tire outer diameter and the rim diameter and measured whenthe tire is mounted on the specified rim, inflated to the specifiedinternal pressure, and in an unloaded state.

“Specified rim” refers to an “applicable rim” defined by the JapanAutomobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim”defined by the Tire and Rim Association, Inc. (TRA), or a “MeasuringRim” defined by the European Tyre and Rim Technical Organisation(ETRTO). Additionally, “specified internal pressure” refers to a“maximum air pressure” defined by JATMA, to the maximum value in “TIRELOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, and to“INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load”refers to a “maximum load capacity” defined by JATMA, the maximum valuein “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined byTRA, or “LOAD CAPACITY” defined by ETRTO. However, in the case of JATMA,for a passenger vehicle tire, the specified internal pressure is an airpressure of 180 kPa, and the specified load is 88% of the maximum loadcapacity.

Additionally, a radial height H4 from the end portion of the turned backportion 132 of the carcass layer 13 to the end portion outward of theouter side reinforcing rubber 19 in the tire radial direction preferablyhas a relationship 0.10≤H4/H2 to the radial height H2 of the contactportion between the body portion 131 and the turned back portion 132 ofthe carcass layer 13, and more preferably has a relationship 0.30≤H4/H2.Thus, the steering stability on dry road surfaces is improved, and thedurability of the bead portion is improved. Note that the upper limit ofthe ratio H4/H2 is subject to restrictions by the upper limit of theratio H3/SH described above.

Additionally, an amount of overlap H5 between the outer side reinforcingrubber 19 and the bead core 11 in the tire radial direction preferablyhas a relationship 0.05≤H5/H1≤1.00 to the radial height H1 of the beadcores 11, and more preferably has a relationship 0.10≤H5/H1≤1.00. Inaddition, the amount of overlap H5 is preferably in a range of 5.0mm≤H5. Accordingly, the amount of overlap H5 between the outer sidereinforcing rubber 19 and the bead core 11 is made appropriate. Inparticular, the lower limit ensures the amount of overlap H5, andsuppresses separation of the rubber at the inner end portion of theouter side reinforcing rubber 19 in the tire radial direction.

The amount of overlap H5 is measured when the tire is mounted on thespecified rim, inflated to the specified internal pressure, and in anunloaded state.

Note that, not limited to the above, the outer side reinforcing rubber19 may be disposed outward in the tire radial direction with respect tothe bead cores 11 (not illustrated).

Additionally, a length T1 of a perpendicular line drawn from the endportion of the turned back portion 132 of the carcass layer 13 to theouter surface of the tire side portion and a thickness T2 of the outerside reinforcing rubber 19 on the perpendicular line preferably have arelationship 0.10≤T2/T1≤0.90, and more preferably have a relationship0.20≤T2/T1≤0.80. Thus, the thickness T2 of the outer side reinforcingrubber 19 is made appropriate. In other words, the lower limitappropriately reinforces the spring characteristics of the bead portionby the outer side reinforcing rubber 19, improves the steering stabilityon dry road surfaces, and improves the durability of the bead portion.In addition, the upper limit suppresses an increase in tire weight dueto the excessive amount of the outer side reinforcing rubber 19.

In addition, in the configuration in which the outer side reinforcingrubber 19 is provided instead of the bead filler as described above, avalue K defined by the following Equation (1) is preferably 0.17≤K, andmore preferably 0.20≤K. Accordingly, the function of the outer sidereinforcing rubber 19 is properly ensured. In Equation (1), W denotes atire nominal width (mm), I denotes a tire nominal inner diameter (inch),and B denotes a total cross-sectional area of bead wires in bead cores(mm²).

$\begin{matrix}{K = \frac{W^{\frac{4}{3}} \times I^{\frac{2}{3}}}{100 \times B^{2}}} & {{Equation}\mspace{14mu} (1)}\end{matrix}$

Note that, in the configuration of FIG. 2, the outer side reinforcingrubber 19 is disposed in the bead portion as described above. However,no such limitation is intended. When the value K described above is lessthan 0.40, the outer side reinforcing rubber 19 may be omitted. Forexample, the rim cushion rubber 17 may have a thick wall structure andmay be disposed so as to fill the region where the outer sidereinforcing rubber 19 is disposed in FIG. 2 (not illustrated).

Rate of Change of Rim Fitting Portion

In the configuration in which bead fillers are omitted as describedabove, the rigidity of the bead portions is reduced, and the rim fittingpressure of the bead portions tends to decrease. For the reason, in theconfiguration of FIG. 2, the bead core 11 has the followingconfiguration to ensure the rim fittability of the tire.

FIG. 3 is an enlarged view illustrating the rim fitting portion of thebead portion illustrated in FIG. 2. FIG. 4 is an explanatory diagramillustrating the wire arrangement structure of the bead coresillustrated in FIG. 3. FIG. 5 is an explanatory diagram illustrating therim fitting portion of the bead portion in a state where the tire ismounted on the rim. In these drawings, FIG. 3 illustrates the rimfitting portion in the state before mounting on the rim, and FIG. 5illustrates the rim fitting portion in a state after mounting on therim. FIG. 4 illustrates a cross-sectional view of the unvulcanized beadcores 11 in the radial direction when the components are alone.

In FIG. 2, the rim fitting surface of the bead portion includes the beadbase Bb, the bead toe Bt, and the bead heel Bh, and has a contour shapeuniform in the tire circumferential direction. The bead base Bb is aflat region formed inward of the bead portion in the tire radialdirection and constitutes a contact surface to the bead sheet 101 of therim. The bead toe Bt is a tip of the bead portion having an L shape or aV shape in the cross-sectional view in the tire meridian direction, andlocated innermost of the rim fitting surface in the tire lateraldirection. The bead heel Bh is a bent portion that connects the wallsurface of the tire side portion to the bead base Bb.

The state before the tire is mounted on the rim (see FIGS. 2 and 3) isdefined as a state when the positions of the right and left beadportions are fixed so as to match measurement points of a rim width anda rim diameter of the specified rim in a state where the tire rotationaxis is horizontalized and the tire alone is disposed upright. Such atire shape is closest to the tire shape in a tire vulcanization mold,that is, a natural tire shape before inflation.

The state after the tire is mounted on the rim (see FIG. 5) is definedas a state when the tire is mounted on the specified rim, inflated tothe specified internal pressure, and in an unloaded state. In the statewhere the tire is mounted on the rim, the rim fitting surfaces of thebead portions fit to the rim 10 of the wheel, thus holding the tire. Atthis time, the bead base Bb of the rim fitting surface is pressedagainst the bead sheet 101 of the rim 10 and brought into surfacecontact. Thus, the fitting portion between the bead portion and the rim10 is sealed, and air tightness inside the tire is ensured.Additionally, the bead heel Bh is located at a connection portionbetween the bead sheet 101 and the flange 102, a region outside the beadheel Bh of the rim fitting surface abuts on the flange 102 of the rim10, and the bead portion is held from outward in the tire lateraldirection.

As illustrated in FIG. 4, in the cross-sectional view in the tiremeridian direction, the bead cores 11 have the predetermined wirearrangement structure in which the wire cross sections of the bead wires111 are arranged. The wire arrangement structure will be describedlater.

Here, in the cross-sectional view in the tire meridian direction in thestate before the tire is mounted on the rim (see FIG. 3), a tangent lineL1 that contacts the innermost layer in the tire radial direction andthe wire cross sections innermost and outermost in the tire lateraldirection in the wire arrangement structure of the bead cores 11 fromthe rim fitting surface side is defined. Contact points C1 and C2 of thetangent line L1 to the respective wire cross sections and the midpointCm of the contact points C1 and C2 are defined. Additionally, gauges Gl,G2, Gm in the tire radial direction from the contact points C1 and C2and the midpoint Cm to the rim fitting surface are defined.Specifically, in the cross-sectional view in the tire meridiandirection, intersection points P1, P2, and Pm between straight linespassing through the contact points Cl, C2, and the midpoint Cm andperpendicular to the tire axial direction and the bead base Bb are eachdrawn up. Distances between the contact points Cl, C2 and the midpointCm and the intersection points P1, P2, and Pm are measured as the gaugesGl, G2, Gm.

Similarly, gauges G1′, G2′, and a Gm′ of the rim fitting portion in thestate after the tire is mounted on the rim (see FIG. 5) are defined.

At this time, rates of change ΔG1, ΔG2, ΔGm of the gauges Gl, G2, Gm ofthe rim fitting portion in the states before and after mounting on therim are each preferably in the range from 10% or greater to 60% or less,more preferably in the range from 15% or greater to 50% or less, furtherpreferably in the range from 20% or greater to 45% or less, and the mostpreferably in the range from 25% or greater to 40% or less. Thus, therates of change ΔG1, ΔG2, ΔGm of the gauges Gl, G2, Gm are set to begreater than those of a typical tire structure including bead fillers.Accordingly, the rates of change ΔG1, ΔG2, ΔGm of the rim fittingportion are made appropriate. That is, the lower limit ensures rimfitting pressure and ensures rim fittability of the tire. Additionally,the upper limit suppresses deterioration of workability of mounting ofthe tire on the rim due to excessive rim fitting pressure.

Using the gauges Gi and Gi′ before and after mounting on the rim at thepredetermined measurement points, a rate of change ΔGi is defined asΔGi=(Gi−Gi′)/Gi×100. For example, using the gauge G1 (see FIG. 3) beforemounting on the rim and the gauge G1′ (see FIG. 5) after mounting on therim, the rate of change ΔG1 is calculated as ΔG1=(G1−G1′)/G1×100.

The rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion describedabove are achieved by, for example, a configuration of a cushion rubberlayer 20 described later (see FIG. 6) and a configuration of a taperangle of the bead base Bb (see FIG. 7).

In addition, the rates of change ΔG1, ΔG2, ΔGm of the rim fittingportion preferably meet the condition of |ΔGm−ΔG2|<|ΔG1−ΔGm|.Accordingly, a difference in rate of change |ΔG1−ΔGm| on the bead toe Btis set greater than a difference in rate of change |ΔGm−ΔG2| on the beadheel Bh. Specifically, the rates of change ΔG1, ΔG2, ΔGm preferably meetthe condition 20%≤|(ΔG1−ΔGm)/(ΔGm−ΔG2)|≤450%, and more preferably meetthe condition 30%≤|(ΔG1−ΔGm)/(ΔGm−ΔG2)|≤300%. Thus, the relationshipbetween the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion ismade appropriate. That is, the lower limit improves the rim fittabilityof the tire. Additionally, the upper limit improves workability ofmounting of the tire on the rim.

In addition, the rates of change ΔG1, ΔG2, ΔGm of the gauges Gl, G2, Gmof the rim fitting portion preferably have a relationship ΔG2<ΔGm<ΔG1.In other words, the rates of change ΔG1, ΔG2, ΔGm increase toward thebead toe Bt. Thus, the rim fittability of the tire is improved.

Additionally, in the configuration of FIG. 3, the gauge G1, G2, Gm ofthe rim fitting portion in the state before mounting the tire on the rimhave a relationship G2<Gm<Gl. In other words, the gauges Gl, G2, Gm ofthe rim fitting portion increase toward the bead toe Bt. Thus, themutual relationship between the rates of change ΔG1, ΔG2, ΔGm is madeappropriate. Additionally, in a passenger vehicle tire, the gauge G1 ispreferably in the range G1≤8.0 mm, and more preferably in the rangeG1≤6.0 mm. Also, the gauges G2 is preferably in the range 1.0 mm≤G2, andmore preferably in the range 2.0 mm≤G2. Thus, the rubber volume of therim fitting portion inward of the bead cores 11 in the radial directionis made appropriate.

Additionally, a width Wc2 (mm) (see FIG. 4) of the innermost layer ofthe wire arrangement structure of the bead cores 11, the rate of changeΔGm (%) at the midpoint Cm, and the tire inner diameter RD (inch) (seeFIG. 2) preferably have a relationship1.0%·mm/inch≤Wc2×ΔGm/RD≤50%·mm/inch, more preferably have a relationship2.0%·mm/inch≤Wc2×ΔGm/RD≤40%·mm/inch, and more preferably have arelationship 5.0%·mm/inch≤Wc2×ΔGm/RD≤30%·mm/inch. Thus, the relationshipbetween the width Wc2 of the innermost layer of the bead cores 11 andthe rate of change ΔGm is made appropriate. That is, the lower limitensures the rim fittability of the tire. Additionally, the upper limitimproves the workability of mounting of the tire on the rim.

As illustrated in FIG. 4, the width Wc2 of the innermost layer of thewire arrangement structure is measured as the maximum width includingthe wire cross sections on the innermost side and the outermost side inthe tire lateral direction.

In addition, the width Wc2 of the innermost layer of the wirearrangement structure is preferably in the range 3.0 mm≤Wc2≤10.0 mm, andmore preferably in the range 4.5 mm≤Wc2≤9.6 mm.

Wire Arrangement Structure of Bead Cores

As illustrated in FIG. 4, the bead cores 11 are formed by annularly andmultiply winding the bead wires 111, and have the predetermined wirearrangement configuration in the cross-sectional view in the tiremeridian direction. The wire arrangement structure is defined by thearrangement of the wire cross sections of the bead wires 111.Additionally, the wire arrangement structure is formed by a plurality oflayers layered in the tire radial direction. These layers are formed ofthe plurality of wire cross-sections arranged in a row in the tirelateral direction. Moreover, the innermost layer of the wire arrangementstructure is substantially parallel to the rim fitting surface of thebead portion and is opposed to the bead sheet 101 of the rim 10 duringfitting of the tire on the rim (see FIG. 3).

In a manufacturing process of the bead cores 11, a core molding jig (notillustrated) is used, and one or a plurality of the bead wires 111 arewound around the core molding jig in the predetermined wire arrangementstructure to mold the unvulcanized bead cores 11. Then, the molded beadcores 11 are pre-vulcanized before a vulcanization molding step of agreen tire. Note that no such limitation is intended, and thepre-vulcanization of the bead cores 11 may be omitted. The unvulcanizedbead cores 11 may be incorporated into the green tire, and thevulcanization molding step of the green tire may be performed.

Additionally, the bead wire 111 is formed of a wire strand and aninsulation rubber covering the wire strand (not illustrated).Additionally, the wire strand is made of steel. Additionally, theinsulation rubber is preferably made of a rubber composition having aMooney viscosity of 70 M or greater. The Mooney viscosity is calculatedin accordance with JIS K6300-1: 2013.

Here, in the configuration of FIG. 2, as described above, the turnedback portion 132 of the carcass layer 13 contacts the body portion 131of the carcass layer 13 to form the closed region X surrounding the beadcores 11. In addition, the rubber occupancy ratio in the closed region Xis set to be small to achieve the weight reduction of the bead portion.At this time, to increase the durability of the bead portion, a cavityportion in the closed region X is preferably suppressed.

Thus, as illustrated in FIG. 4, the wire arrangement structure of thebead cores 11 has a wedge shape that protrudes toward outward in thetire radial direction. Specifically, a layer in which the number ofarrangements of the wire cross sections is the maximum in the wirearrangement structure (in FIG. 4, the second layer from the innermostlayer) is defined as the maximum arrangement layer. At this time, thenumber of layers of the wire cross sections outward in the tire radialdirection with respect to the maximum arrangement layer (three layers inFIG. 4) is greater than the number of layers of the wire cross sectionsinward in the tire radial direction with respect to the maximumarrangement layer (one layer in FIG. 4). Additionally, the number ofarrangements of the wire cross sections in each layer outward in thetire radial direction with respect to the maximum arrangement layermonotonically decreases outward in the tire radial direction from themaximum arrangement layer. Furthermore, the number of layers of the wirecross sections is preferably in the range from four or greater to six orless. Additionally, the number of arrangements of the wire crosssections in the maximum arrangement layer in the wire arrangementstructure is preferably four or five, and the number of arrangements ofthe wire cross sections in the outermost layer in the tire radialdirection is preferably one or two.

The wire cross sections are preferably arranged in a closest-packedstructure in the region outward in the tire radial direction withrespect to the maximum arrangement layer. The “closest-packed structure”refers to a state in which centers of the three adjacent wire crosssections are arranged to form a substantially equilateral triangle inthe cross-sectional view in the tire meridian direction. In such aclosest-packed structure, disposal density of the wire cross sections ofthe bead cores 11 is increased and a core-collapse resistance of thebead cores 11 is improved compared to a lattice arrangement structure inwhich the rows of the wire cross sections are orthogonal vertically andhorizontally. Note that, in the closest-packed state, it is notnecessary for all sets of the adjacent wire cross sections to come intocontact with one another, and some sets may be disposed with fine gaps(not illustrated).

In such a configuration, as illustrated in FIG. 3, the body portion 131and the turned back portion 132 of the carcass layer 13 extend outwardin the tire radial direction along the wedge shape of the wirearrangement structure while abutting on the right and left side surfacesin the tire lateral direction of the bead cores 11, and are joined in aY-shape to come into contact with one another. Thus, a gap between thejoining portion of the body portion 131 with the turned back portion 132of the carcass layer 13 and the top portion (so-called bead top) outwardof the bead core 11 in the tire radial direction becomes small, and thedurability of the bead portion is improved. In particular, the structurein which bead fillers are omitted described above is preferred in thatthe rubber occupancy ratio in the closed region X can be reduced. Inaddition, since the turned back portion 132 can bend at an obtuse angleat the joining position with the body portion 131, the amount of bendingof the turned back portion 132 becomes small, and the durability of thebead portion is improved.

The number of arrangements of the wire cross sections in the innermostlayer in the tire radial direction in the wire arrangement structure ispreferably three or four, and is preferably same as or smaller than thenumber of arrangements of the wire cross sections in the maximumarrangement layer.

As illustrated in FIG. 4, arrangement angles θ1, θ2 of the wire crosssections at corner portions inward in the tire radial direction andinward and outward in the tire lateral direction in the wire arrangementstructure are each defined. At this time, the arrangement angles θ1, θ2are in the range 80 degrees≤θ1, and 80 degrees≤θ2. That is, thearrangement angles θ1, θ2 of the wire cross sections form substantiallyright angles or obtuse angles. In addition, as illustrated in FIG. 4,the arrangement angles θ1, θ2 of the wire cross sections are preferablyin the range 100 degrees≤θ1≤150 degrees, and 100 degrees≤θ2≤150 degrees.Thus, disruption of the wire arrangement structure during tirevulcanization is suppressed, the rim fittability of the tire isimproved, and the durability of the bead portion is improved. Also, whenthe arrangement angles θ1, θ2 of the wire cross sections have the obtuseangles, the carcass ply can be turned back along the corner portionsinward of the bead cores 11 in the tire radial direction. Accordingly,the rubber occupancy ratio in the closed region X can be reduced, andthe weight of the bead portion can be reduced further.

The arrangement angles θ1, θ2 are measured as angles formed by linesconnecting the centers of the three wire cross-sections constituting thecorner portions of the wire arrangement structure.

Additionally, in FIG. 4, a maximum width Wc1 and a maximum height Hc1 ofthe bead cores 11 and a total cross-sectional area S of the bead wires111 in the bead cores 11 preferably have a relationship 1.20≤Wc1×He1/S≤5.00, more preferably have a relationship 1.50≤Wc1×Hc1/S≤4.50, andmore preferably have a relationship 1.80≤Wc1×Hc1/S≤4.00. Thus, the wirearrangement structure of the bead cores 11 is made appropriate. That is,the lower limit ensures the number of arrangements of the wire crosssections, and ensures the rim fittability of the tire. In addition, theupper limit reduces the weight of the bead cores 11.

Note that the total cross-sectional area S of the bead wires does notinclude the cross-sectional area of the insulation rubbers.

Furthermore, the total cross-sectional area S of the bead wires 111 ispreferably in the range 5 mm²≤S≤35 mm², more preferably in the range 6mm²≤S≤32 mm², and further preferably in the range 7 mm²≤S≤28 mm². Thus,the total cross-sectional area S of the bead wires 111 is madeappropriate. Specifically, the lower limit ensures the totalcross-sectional area S of the bead wires 111 and ensures the rimfittability of the tire. In addition, the upper limit reduces the weightof the bead cores 11.

In addition, an outer diameter φ (see FIG. 4) of the bead wire 111 ispreferably in the range 0.8 mm≤φ≤1.5 mm, and more preferably in therange 0.9 mm≤φ≤1.4 mm, and further preferably in the range 1.0 mm≤φ≤1.3mm Thus, the outer diameter φ of the bead wire 111 is made appropriate.That is, the lower limit ensures the outer diameter φ of the bead wire111, and ensures the rim fittability of the tire. In addition, the upperlimit reduces the weight of the bead cores 11.

Additionally, in FIG. 4, a height Hc2 from the tangent line L1 of theinnermost layer in the wire arrangement to the maximum width position ofthe bead cores 11, and the maximum height Hc1 of the bead cores 11preferably have a relationship 1.10≤(Hc1−Hc2)/Hc2≤2.80, and preferablyhave a relationship 1.30≤(Hc1−Hc2)/Hc2≤2.50, and more preferably have arelationship 1.50≤(Hc1−Hc2)/Hc2≤2.30. Thus, the wire arrangementstructure of the bead cores 11 is made appropriate.

The maximum height Hc1 of the bead cores is measured as the maximumheight of the bead cores from the tangent line L1.

The height Hc2 of the widest position of the bead cores is measured as adistance between the tangent line L1 and an imaginary line connectingthe centers of the wire cross sections constituting the maximumarrangement layer. In a configuration in which the wire arrangementstructure includes the plurality of maximum arrangement layers, themaximum arrangement layer on the outermost side in the tire radialdirection is used to measure the height Hc2 of the maximum widthposition.

For example, in the configuration of FIG. 4, the number of layers of thewire cross sections is five, and the number of arrangements of the wirecross sections is set to 3-4-3-2-1 in the order from the innermost layerin the tire radial direction. Thus, the number of arrangements of thewire cross sections in the maximum arrangement layer is four.Additionally, the number of layers of the wire cross sections outward inthe tire radial direction with respect to the maximum arrangement layeris three, and the number of layers of the wire cross sections inward inthe tire radial direction with respect to the maximum arrangement layeris one. Accordingly, the maximum arrangement layer is asymmetric in thetire radial direction and disposed so as to be biased inward in the tireradial direction with respect to the center position in the tire radialdirection of the wire arrangement structure. The wire arrangementstructure has a structure long outward in the tire radial direction fromthe maximum arrangement layer. Moreover, the number of arrangements ofthe wire cross sections in each layer decreases one by one outward inthe tire radial direction from the maximum arrangement layer. Also, allwire cross-sections are arranged in the closely-packed structure. Thus,both of the arrangement angles θ1, θ2 of the wire cross sections at theleft and right corner portions in the tire radial direction of the wirearrangement structure are approximately 135 degrees (specifically, inthe range from 130 degrees to 140 degrees). Moreover, the maximumarrangement layer of the wire cross-sections is not the innermost layerin the tire radial direction. In addition, the number of arrangements ofthe wire cross sections in each layer increases one by one from theinnermost layer to the maximum arrangement layer. This optimizes thewire arrangement structure.

Additionally, in FIG. 3, a distance Hg in the tire radial direction fromthe end portion outward of the bead cores 11 in the tire radialdirection to the contact portion between the body portion 131 and theturned back portion 132 of the carcass layer 13 preferably has arelationship Hg/φ≤7.0 to the outer diameter φ of the bead wire 111, andmore preferably has a relationship Hg/φ≤3.0. Thus, the rigidity aroundthe bead cores 11 is improved. Note that the lower limit of the ratioHg/φ is 0≤Hg/φ in the case of Hg=0.

Gauges of Rim Fitting Portion

FIG. 6 is an explanatory diagram illustrating the rim fitting portionillustrated in FIG. 3. The same drawing illustrates the rim fittingportion in the state before mounting on the rim. In the same drawing,constituents that are the same as constituents illustrated in FIG. 3have the same reference signs, and explanations thereof are omitted.

In FIG. 6, as described above, the gauge G2 in the tire radial directionfrom the contact point C2 between the tangent line L1 of the innermostlayer of the wire arrangement and the wire cross section outermost inthe tire lateral direction to the rim fitting surface is defined. Atthis time, the gauge G2 and the outer diameter φ (see FIG. 4) of thebead wire 111 preferably have a relationship 1.3≤G2/φ≤9.5, and morepreferably have a relationship 1.8≤G2/φ≤5.5. Thus, the gauge G2 of therim fitting portion is made appropriate. Specifically, the lower limitensures the gauge G2 of the rim fitting portion and ensures the rimfittability of the tire. Additionally, the upper limit suppressesdeterioration of workability of mounting of the tire on the rim due tothe excessive gauge G2 of the rim fitting pressure.

Additionally, in FIG. 6, an intersection point Q between a straight linepassing through the contact point C2 of the bead core 11 and parallel tothe tire lateral direction and a wall surface outward of the rim fittingportion in the tire lateral direction is defined. Also, a gauge Wh inthe tire lateral direction from the contact point C2 of the bead core 11to the point Q at the rim fitting surface is defined. At this time, thegauge Wh and the outer diameter φ (see FIG. 4) of the bead wire 111preferably have a relationship 2.0≤Wh/φ≤15.0, and more preferably have arelationship 2.5≤Wh/φ≤10.0. Thus, the gauge Wh of the rim fittingportion is made appropriate. That is, the lower limit ensures the gaugeWh of the rim fitting portion, ensures the rim fittability of the tire,and ensures the durability of the rim fitting portion. Additionally, theupper limit suppresses deterioration of workability of mounting of thetire on the rim due to the excessive gauge Wh of the rim fittingpressure.

Additionally, as illustrated in FIG. 6, the cushion rubber layer 20 isinserted between the innermost layer of the bead cores 11 and the rimcushion rubber 17. The cushion rubber layer 20 is a member having arubber hardness lower than that of the rim cushion rubber 17, includes,for example, the innerliner 18 and a tie rubber (not illustrated) thatbonds the innerliner 18 and the carcass layer 13 together, and does notinclude the carcass ply. Additionally, the cushion rubber layer 20 mayhave an integral structure with the innerliner 18 and the tie rubber, ormay have a separate structure (not illustrated).

Additionally, the cushion rubber layer 20 may be made of a rubbermaterial same as those of the innerliner 18 and the tie rubber describedabove, or may be made of a different rubber material (not illustrated).The cushion rubber layer 20 traverses a range from the contact point C1to the midpoint Cm of the bead cores 11 in the tire lateral direction,and preferably a range from the contact point C1 to the contact pointC2. In such a configuration, the cushion rubber layer 20 is interposedbetween the innermost layer of the bead cores 11 and the rim fittingsurface of the bead portion. This increases the rates of change ΔG1,ΔG2, ΔGm of the rim fitting portion, thus improving the rim fittabilityof the tire. Additionally, the contact pressure of the rim fittingsurface to the rim 10 is made uniform.

Additionally, the rubber hardness of the cushion rubber layer 20 ispreferably lower than the rubber hardness of the rim cushion rubber 17by five or greater and more preferably eight or greater. Thus, theeffect of increasing the rates of change ΔG1, ΔG2, ΔGm of the rimfitting portion is appropriately obtained.

For example, in the configuration of FIG. 6, in the cross-sectional viewin the tire meridian direction, the cushion rubber layer 20 extendsoutward in the tire lateral direction from the tire cavity surface alongthe turned back portion 132 of the carcass layer 13 and is interposedbetween the bead cores 11 and the rim cushion rubber 17. Also, thecushion rubber layer 20 extends up to the outermost contact point C2beyond the midpoint Cm of the innermost layer of the bead cores 11.Additionally, the end portion outward of the cushion rubber layer 20 inthe tire lateral direction terminates inward in the tire radialdirection with respect to the tangent line L1 of the bead cores 11.Accordingly, the end portion of the cushion rubber layer 20 does notextend up to the side surface outward of the bead cores 11 in the tirelateral direction. Thus, the rates of change ΔG1, ΔG2, ΔGm between thebead cores 11 and the rim fitting surface (in particular, the bead baseBb) are effectively increased while the rigidity between the bead cores11 and the flange 102 (see FIG. 2) of the rim 10 is properly ensured.However, no such limitation is intended, and the end portion outward ofthe cushion rubber layer 20 in the tire lateral direction may extend upto outward in the tire radial direction with respect to the tangent lineL1 of the bead cores 11.

Additionally, in FIG. 6, thicknesses Tc1, Tc2 of the cushion rubberlayer 20 in between the measurement points C1 and P1; and C2 and P2 ofthe gauges Gl, G2 of the rim fitting portion preferably have arelationship Tc2<Tc1. In other words, the thickness Tc1 of the cushionrubber layer 20 on the bead toe Bt side is preferably thicker than thethickness Tc2 of the cushion rubber layer 20 on the bead heel Bh side.Thus, the rate of change ΔG1 of the rim fitting portion on the bead toeBt side becomes greater than the rate of change ΔG2 of the rim fittingportion on the bead heel Bh side (ΔG2<ΔG1), and the rim fittability ofthe tire is improved.

Additionally, as described above, adjusting the relationship of thethicknesses of the cushion rubber layer 20 in between the measurementpoints Cl and P1; C2 and P2; and Cm and Pm of the gauges Gl, G2, Gm ofthe rim fitting portion allows adjusting the relationship between therates of change ΔG1, ΔG2, ΔGm of the rim fitting portion.

Additionally, an average value of the thicknesses of the cushion rubberlayer 20 in the region in the tire lateral direction from the contactpoint C1 to the contact point C2 is preferably in the range from 0.3 mmor greater to 3.0 mm or less. Thus, the average thickness of the cushionrubber layer 20 is made appropriate. In other words, the lower limitappropriately obtains the effect of the cushion rubber layer 20 thatincreases the rates of change ΔG1, ΔG2, ΔGm of the rim fitting portion.Additionally, the upper limit suppresses the decrease in rigidity of therim fitting portion caused by the excessive amount of the cushion rubberlayer 20.

Additionally, in FIG. 6, the gauge G1 of the rim fitting portion on thebead toe Bt side and the thickness Tc1 of the cushion rubber layer 20preferably have a relationship 0.03≤Tc1/G1≤0.95, and more preferablyhave a relationship 0.05≤Tc1/G1≤0.85. Thus, the average thickness of thecushion rubber layer 20 is made appropriate. That is, the lower limitproperly ensures the effect of the cushion rubber layer 20, andincreases the rate of change ΔG1 of the rim fitting portion.Additionally, the upper limit ensures the gauge G1 of the rim cushionrubber 17, and properly ensures the rim fittability of the tire.Additionally, on the tire cavity portion side, the cushion rubber layer20 extends outward in the tire radial direction from the measurementpoint of the height H1 (see FIG. 2) of the bead cores 11 outward in thetire radial direction preferably by 5 mm or greater.

Shape of Rim Fitting Surface

FIG. 7 is an explanatory diagram illustrating the rim fitting portionillustrated in FIG. 3. The same drawing illustrates the rim fittingportion in the state before mounting on the rim. In the same drawing,constituents that are the same as constituents illustrated in FIG. 3have the same reference signs, and explanations thereof are omitted.

As illustrated in FIG. 7, in the cross-sectional view in the tiremeridian direction in the state before mounting on the rim, a tangentline of the rim fitting surface at an intersection point P2 is definedas an extension line L2 of the bead base Bb.

At this time, an inclination angle α of the extension line L2 of thebead base Bb with respect to the tangent line L1 of the bead cores 11 ispreferably in the range 3 degrees≤α≤15 degrees, and more preferably inthe range 6 degrees≤α≤12 degrees.

Additionally, the inclination angle α (degree) of the extension line L2of the bead base Bb, the rate of change ΔGm (%) of the rim fittingportion, and a tire nominal width WA (dimensionless) preferably have arelationship 0%·degree≤ΔGm×α/WA≤7%·degree, and more preferably have arelationship 0.5%·degree≤ΔGm×α/WA≤5.0%·degree. Thus, a ratio ΔGm×α/WAindicative of the rim fittability of the tire is made appropriate. Inother words, in general, as the tire nominal width WA becomes large, therim fittability of the tire tends to be low. Additionally, the greaterthe inclination angle α of the bead base Bb and the rate of change ΔGmof the rim fitting portion, the greater the fitting pressure to the rim,thus improving the rim fittability of the tire. Accordingly, the lowerlimit increases the ratio ΔGm×α/WA, and improves the rim fittability ofthe tire. Additionally, the upper limit suppresses deterioration ofworkability of mounting of the tire on the rim due to excessive fittingpressure to the rim. Note that when the inclination angle α=0 degrees,ΔGm×α/WA=0 is met.

Additionally, as illustrated in FIG. 7, in the cross-sectional view inthe tire meridian direction, when the bead base Bb has a shape formed byconnecting the two types of linear portions with the mutually differentinclination angles (so-called two-stage tapered shape), the extensionline L2 of the linear portion on the bead heel Bh side and an extensionline L3 of the linear portion on the bead toe Bt side of the bead baseBb of the rim fitting surface are defined.

At this time, the inclination angles α, β of the extension lines L2 andL3 of the bead base Bb with respect to the tangent line L1 of the beadcores 11 preferably have a relationship 0≤β/α≤5.0, and more preferablyhave a relationship 1.8≤β/α≤4.0. Thus, the two-stage tapered shape ofthe bead base Bb is made appropriate. In other words, the lower limitappropriately obtains the effect of improving the rim fittability of thetire brought by the two-stage tapered shape. Additionally, the upperlimit suppresses the occurrence of vulcanization failure in the beadbase Bb.

Additionally, in FIG. 7, the intersection point R of the two types oflinear portions of the bead base Bb is defined.

At this time, a distance Lr in the tire lateral direction from the beadtoe Bt to the intersection point R and a distance Lm in the tire lateraldirection from the bead toe Bt to the midpoint Cm preferably have arelationship 0.50≤Lr/Lm≤4.0, and more preferably have a relationship0.70≤Lr/Lm≤3.3. Thus, the position of the intersection point R is madeappropriate, and the effect of improving the rim fittability of the tirebrought by the two-stage tapered shape is appropriately obtained.

For example, in the configuration of FIG. 7, the arrangement angle θ1(see FIG. 4) of the wire cross sections at the corner portion inward inthe tire radial direction and inward in the tire lateral direction ofthe wire arrangement of the bead cores 11 is in the range from 130degrees or greater to 140 degrees or less. Additionally, the two typesof linear portions of the bead base Bb are connected with a smooth arcthat protrudes outward in the tire radial direction. Also, theintersection point R is located between the contact point C1 and themidpoint Cm of the bead cores 11.

In FIG. 7, a distance Dt in the tire radial direction from the contactpoint C1 of the bead cores 11 to the bead toe Bt and a distance Wt inthe tire lateral direction are each defined. At this time, the distancesDt, Wt and the gauge G1 in the tire radial direction from the contactpoint C1 to the rim fitting surface preferably have a relationship 7degrees≤arctan {(Dt−G1)/Wt}≤30 degrees, and more preferably have therelationship 9 degrees≤arctan {(Dt−G1)/Wt}≤25 degrees. Thus, a gradientof the rim fitting surface with respect to the tire axial direction fromthe bead cores 11 to the bead toe Bt is made appropriate. That is, thelower limit ensures the gradient of the rim fitting surface, and ensuresthe rim fittability of the tire. Additionally, the upper limitsuppresses a decrease in workability of mounting of the tire on the rimdue to excessive gradient of the rim fitting surface.

The distance Dt from the contact point C1 to the bead toe Bt and thedistance Wt are measured in the state before mounting of the tire on therim. Modified Examples

FIGS. 8 to 12 are explanatory diagrams illustrating the modifiedexamples of the bead cores illustrated in FIG. 4. These drawingsillustrate a cross-sectional view of the unvulcanized bead cores 11 inthe radial direction when the components are alone.

In the configuration of FIG. 4, the tangent line L1 to the innermostlayer of the bead cores 11 is parallel to the tire lateral direction.Accordingly, the inclination angle X of the tangent line L1 with respectto the tire lateral direction is X=0 degrees.

However, no such limitation is intended, and as illustrated in FIG. 8,the bead cores 11 may be inclined to the tire lateral direction.Specifically, the bead cores 11 may be inclined inward in the tireradial direction on the bead toe Bt (see FIG. 3) side. In such aconfiguration, the tangent line L1 of the innermost layer of the beadcores 11 approaches the bead base Bb of the rim fitting surface inparallel. At this time, the inclination angle X of the tangent line L1with respect to the tire lateral direction is preferably in the rangefrom −10 degrees≤X≤30 degrees. Note that the range of the relativeinclination angle α of the extension line L2 of the bead base Bb withrespect to the tangent line L1 of the bead cores 11 is as describedabove.

Additionally, in the configuration of FIG. 4, as described above, thenumber of arrangements of the wire cross sections is set to 3-4-3-2-1 inthe order from the innermost layer in the tire radial direction. Thus,the number of layers of the wire cross sections is five, and the numberof arrangements of the wire cross sections in the outermost layer in thetire radial direction is one.

In contrast, in the configuration of FIG. 9, the number of layers of thewire cross-sections is four, and the number of arrangements of the wirecross sections is set to 3-4-3-2 in the order from the innermost layerin the tire radial direction. In the configuration illustrated in FIG.10, the number of layers of the wire cross-sections is six, and thenumber of arrangements of the wire cross sections is set to 3-4-5-4-3-2in the order from the innermost layer in the tire radial direction.Thus, the number of layers of the wire cross sections may be four orsix. Additionally, the number of arrangements of the wire cross sectionsof the outermost layer in the tire radial direction may be two. In suchcases, the numbers of layers of the wire cross sections outward in thetire radial direction with respect to the maximum arrangement layer (twolayers in FIG. 9 and three layers in FIG. 10) are greater than thenumbers of layers of the wire cross sections inward in the tire radialdirection with respect to the maximum arrangement layer (one layer inFIG. 9 and two layers in FIG. 10). Moreover, the number of arrangementsof the wire cross sections in each layer decreases one by one outward inthe tire radial direction from the maximum arrangement layer.

Additionally, in the configuration of FIG. 4, the number of arrangementsof the wire cross sections in the innermost layer in the tire radialdirection is less than the number of arrangements of the wire crosssections in the maximum arrangement layer (the second layer from theinnermost layer). Also, all wire cross-sections that constitute the wirearrangement structure are arranged in the closely-packed structure.Thus, both of the arrangement angles θ1, θ2 of the wire cross sectionsat the corner portions inward in the tire radial direction and inwardand outward in the tire lateral direction in the wire arrangementstructure are in the range from 130 degrees or greater to 140 degrees orless.

In contrast, in the configuration of FIGS. 11 and 12, the number oflayers of the wire cross sections is five, and the number ofarrangements of the wire cross sections is set to 4-4-3-2-1 in the orderfrom the innermost layer in the tire radial direction. Thus, the numberof arrangements of the wire cross sections in the innermost layer is thesame as the number of arrangements of the wire cross sections in themaximum arrangement layer. Additionally, in the configuration of FIG.11, the arrangement angle θ1 of the wire cross sections at the cornerportion inward in the tire radial direction and inward in the tirelateral direction of the wire arrangement structure has an acute angle,and is in the range from 55 degrees or greater to 65 degrees or less. Onthe other hand, the arrangement angle θ2 of the wire cross sections atthe corner portion outward in the tire lateral direction has an obtuseangle and is in the range from 130 degrees or greater to 140 degrees orless. In the configuration illustrated in FIG. 12, both of thearrangement angles θ1, θ2 of the wire cross sections at the left andright corner portions inward in the tire radial direction of the wirearrangement structure have substantially right angles, and are in therange from 85 degrees or greater to 95 degrees or less. In this manner,at least the arrangement angle θ2 of the wire cross sections at thecorner portion outward in the tire lateral direction preferably has thesubstantially right angle or obtuse angle. In the configurationillustrated in FIG. 12, the wire cross sections are arranged in alattice shape inward from the maximum arrangement layers in the tireradial direction. In this manner, it is sufficient that the wire crosssections be arranged in the closely-packed structure at least in eachlayer outward from the maximum arrangement layers in the tire radialdirection.

Gauge of Tire Side Portion

FIG. 13 is an enlarged view illustrating the tire side portion of thepneumatic tire illustrated in FIG. 1. The same drawing illustrates anenlarged cross-sectional view in the tire meridian direction at a tiremaximum width position A.

In FIG. 13, a total thickness K1 of the tire side portion at the tiremaximum width position A is preferably in the range 2.5 mm≤K1≤6.5 mm,and more preferably in the range 3.0 mm≤K1≤6.0 mm. Thus, the totalthickness K1 of the tire side portion is made appropriate. That is, thelower limit ensures the total thickness K1 of the tire side portion, andensures a tire rolling resistance. Also, the upper limit ensures theweight reduction of the tire.

The total thickness K1 of the tire side portion is measured as adistance between the tire inner surface and the tire outer surface atthe tire maximum width position A in the cross-sectional view in thetire meridian direction.

In addition, a thickness K2 of a sidewall rubber 16 at the tire maximumwidth position A is preferably in the range 0.3 mm≤K2≤3.0 mm, and morepreferably in the range 0.5 mm≤K2≤2.5 mm. Thus, the thickness K2 of thesidewall rubber 16 is made appropriate. That is, the lower limit ensuresthe thickness K2 of the sidewall rubber 16 and ensures a cut resistanceof the tire side portion. Also, the upper limit ensures the weightreduction of the tire.

Effects

As described above, the pneumatic tire 1 includes the bead cores 11, thecarcass layer 13, and the rim cushion rubber 17. The bead cores 11 areformed by annularly and multiply winding one or a plurality of the beadwires 111. The carcass layer 13 is formed of the carcass ply of a singlelayer or a plurality of layers. The carcass layer 13 is turned back soas to wrap the bead cores 11 and extended between the bead cores 11. Therim cushion rubber 17 is disposed along the turned back portion 132 ofthe carcass layer 13 to constitute the rim fitting surface of the beadportion (see FIGS. 1 and 2). The turned back portion 132 of the carcasslayer 13 contacts the body portion 131 of the carcass layer 13 in thecross-sectional view in the tire meridian direction to form the closedregion X surrounding the bead cores 11 (see FIG. 2). The rubberoccupancy ratio in the closed region X is in the range of 15% or less.The bead cores 11 have the predetermined wire arrangement structureformed by arranging the wire cross sections of the bead wires 111 in thecross-sectional view in the tire meridian direction (see FIG. 4). Thetangent line L1 that contacts the innermost layer in the tire radialdirection and the wire cross sections innermost and outermost in thetire lateral direction in the wire arrangement structure from the rimfitting surface side, and the contact point C2 of the tangent line L1 onthe wire cross section on the outermost are defined (see FIG. 6). Atthis time, the gauge Wh in the tire lateral direction from the contactpoint C2 to the rim fitting surface and the outer diameter φ of the beadwire have a relationship 2.0≤Wh/φ≤15.0. Additionally, the radial heightH2 of the contact portion between the body portion 131 and the turnedback portion 132 of the carcass layer 13 has the relationship0.80≤H2/H1≤3.00 to the radial height H1 of the bead cores 11.

In such a configuration, (1) the rubber occupancy ratio in the closedregion X surrounded by the body portion 131 and the turned back portion132 of the carcass layer 13, that is, the rubber volume around the beadcores 11, is set to be considerably low. Thus, since bead fillers can beomitted, the weight of the tire can be reduced. Thus, (2) the ratio Wh/φbrings an advantage that the gauge Wh of the rim fitting portion is madeappropriate. That is, the lower limit ensures the gauge Wh of the rimfitting portion and ensures the durability of the rim fitting portion.Additionally, the upper limit suppresses deterioration of workability ofmounting of the tire on the rim due to the excessive gauge Wh of the rimfitting pressure. Additionally, (3) the range of H2/H1 brings anadvantage that the radial height H2 of the self-contact portion of thecarcass layer 13 is made appropriate. In other words, the lower limitcauses the turned back portion 132 to be stably supported to the bodyportion 131, thus improving durability of the bead portion. In addition,the upper limit suppresses an increase in tire weight due to theexcessive amount of the turned back portion 132.

Additionally, in the pneumatic tire 1, a layer in which the number ofarrangements of the wire cross sections is the maximum in the wirearrangement structure (in FIG. 4, the second layer from the innermostlayer) is defined as the maximum arrangement layer. At this time, thenumber of layers of the wire cross sections outward in the tire radialdirection with respect to the maximum arrangement layer (three layers inFIG. 4) is greater than the number of layers of the wire cross sectionsinward in the tire radial direction with respect to the maximumarrangement layer (one layer in FIG. 4). Additionally, the number ofarrangements of the wire cross sections in each layer outward in thetire radial direction with respect to the maximum arrangement layermonotonically decreases outward in the tire radial direction from themaximum arrangement layer (see FIG. 4). This has an advantage that a gapbetween the joining portion of the body portion 131 with the turned backportion 132 of the carcass layer 13 and the top portion (so-called beadtop) outward of the bead core 11 in the tire radial direction becomessmall, and the durability of the bead portion is improved. Inparticular, the structure in which bead fillers are omitted describedabove is preferred in that the rubber occupancy ratio in the closedregion X can be reduced. In addition, there is an advantage that, sincethe turned back portion 132 can bend at an obtuse angle at the joiningposition with the body portion 131, the amount of bending of the turnedback portion 132 becomes small, and the durability of the bead portionis improved.

Additionally, in the pneumatic tire 1, the arrangement angle θ2 of thewire cross sections at the corner portion inward in the tire radialdirection and outward in the tire lateral direction of the wirearrangement structure is in the range 80 degrees≤θ2 (see FIG. 4). Thishas an advantage that disruption of the wire arrangement structureduring tire vulcanization is suppressed, and the durability of the beadportion is improved.

Additionally, in the pneumatic tire 1, the arrangement angle θ2 of thewire cross sections at the corner portion inward in the tire radialdirection and outward in the tire lateral direction of the wirearrangement structure is in the range 100 degrees≤θ2≤150 degrees (seeFIG. 4). This has an advantage that disruption of the wire arrangementstructure during tire vulcanization is suppressed, and the durability ofthe bead portion is improved.

Additionally, in the pneumatic tire 1, the actual length La2 of thecontact portion between the body portion 131 and the turned back portion132 of the carcass layer 13 has the relationship 0.30≤La2/La1≤2.00 withrespect to the circumferential length La1 of the closed region. Thus,the actual length La2 of the self-contact portion of the carcass layer13 is made appropriate. That is, the lower limit properly ensures springcharacteristics of the carcass layer 13 and ensures the durability ofthe bead portion. In addition, the upper limit suppresses an increase intire weight due to the excessive amount of the turned back portion 132.

Additionally, the pneumatic tire 1 includes the outer side reinforcingrubber 19. The outer side reinforcing rubber 19 has the rubber hardnesshigher than the rubber hardness of the rim cushion rubber 17, and isdisposed between the turned back portion 132 of the carcass layer 13 andthe rim cushion rubber 17 (see FIG. 2). The configuration, particularlythe configuration in which bead fillers are omitted described above, isadvantageous that the spring characteristics of the bead portion arereinforced by the outer side reinforcing rubber 19 and the durability ofthe bead portion is ensured.

Additionally, in the pneumatic tire 1, the difference ΔHs_RC between therubber hardness of the rim cushion rubber 17 and the rubber hardness ofthe outer side reinforcing rubber 19 is three or greater. This has anadvantage that the reinforcing effect of the spring characteristics ofthe bead portion caused by the outer side reinforcing rubber 19 isappropriately exhibited.

Additionally, in the pneumatic tire 1, when the tire nominal width W(mm), the tire nominal inner diameter I (inch), and the totalcross-sectional area B (mm²) of the bead wires 111 in the bead cores 11are defined, the value K defined by Equation (1) above is in the range0.17≤K. This has an advantage that the function of the outer sidereinforcing rubber 19 is properly ensured.

Additionally, in the pneumatic tire 1, the radial height H3 (see FIG. 2)from the measurement point of the tire inner diameter RD to the endportion outward of the outer side reinforcing rubber 19 in the tireradial direction and the tire cross-sectional height SH (see FIG. 1)have the relationship 0.10≤H3/SH≤0.60. This has an advantage that theradial height H3 of the outer side reinforcing rubber 19 is madeappropriate. In other words, the lower limit appropriately reinforcesthe spring characteristics of the bead portion by the outer sidereinforcing rubber 19, and improves the durability of the bead portion.In addition, the upper limit suppresses the increase in tire weight dueto the excessive amount of the outer side reinforcing rubber 19.

Additionally, in the pneumatic tire 1, the outer side reinforcing rubber19 covers the end portion of the turned back portion 132 of the carcasslayer 13 from outward in the tire lateral direction (see FIG. 2). Thishas an advantage that stress concentration on the end portion of theturned back portion 132 is reduced and the durability of the beadportion is improved.

Additionally, in the pneumatic tire 1, the radial height H4 from the endportion of the turned back portion 132 of the carcass layer 13 to theend portion outward of the outer side reinforcing rubber 19 in the tireradial direction has the relationship 0.30≤H4/H2 to the radial height H2of the contact portion between the body portion 131 and the turned backportion 132 of the carcass layer 13 (see FIG. 2). This has an advantagethat the reinforcing effect of the bead portion can be obtained at apart fixed with a flange 102 of the wheel 10 and a part at and near aboundary with a part separated from the rim flange (that is, a positionwhere a deformation of the tire increases and flexural fatigue is likelyto occur) in the state that the tire is mounted on the rim and thedurability of the bead portion is improved.

Additionally, in the pneumatic tire 1, the length T1 of theperpendicular line drawn from the end portion of the turned back portion132 of the carcass layer 13 to the outer surface of the tire sideportion and the thickness T2 of the outer side reinforcing rubber 19 onthe perpendicular line have the relationship 0.10≤T2/T1≤0.90. This hasan advantage that the thickness T2 of the outer side reinforcing rubber19 is made appropriate. In other words, the lower limit appropriatelyreinforces the spring characteristics of the bead portion by the outerside reinforcing rubber 19, and improves the durability of the beadportion. In addition, the upper limit suppresses the increase in tireweight due to the excessive amount of the outer side reinforcing rubber19.

Additionally, in the pneumatic tire 1, the height Hc2 from the tangentline L1 to the maximum width position of the bead cores 11 and themaximum height Hc1 of the bead cores 11 have the relationship1.10≤(Hc1−Hc2)/Hc2≤2.80 (see FIG. 4). This has an advantage that thewire arrangement structure of the bead cores 11 is made appropriate.

Example

FIG. 14 is a table showing results of performance tests of pneumatictires according to the embodiment of the technology. FIG. 15 is anexplanatory diagram illustrating bead cores of a test tire ofConventional Example.

In the performance test, a plurality of types of test tires having atire size of 205/55R16 were evaluated for (1) tire mass and (2)durability.

(1) The tire mass is calculated as the average value of the masses offive test tires having the same structure. The measurement results areexpressed as index values and evaluated with the Conventional Examplebeing assigned as the reference (100). The smaller the values in thisevaluation, the lighter the test tires are, which is preferred.Additionally, when the index is 99 or less, it can be said that theweight of the tire is reduced compared to that of the existing tirestructure including bead fillers.

(2) In the evaluation for durability, the test tires are mounted on rimshaving a rim size of 16×6.5 J, and the test tires are inflated to an airpressure of 230 kPa. In addition, a drum testing machine with a diameterof 1707 mm is used, and under test conditions of a circumferentialtemperature of 38±3° C. and a running speed of 81 km/h, an applied loadis increased by 13% at every two hours from the maximum load of 88%specified by JATMA, and the total travel distance until the test tire isbroken is measured. The measurement results are expressed as indexvalues and evaluated with the Conventional Example being assigned as thereference (100). In this evaluation, larger values are preferable.

The test tires of Examples 1 to 9 achieve the weight reduction of thetires by having the structures of omitting bead fillers (see FIGS. 1 and2). Additionally, the gauges Gl, Gm, and G2 of the rim fitting portionin the state before mounting on the rim have a relationship G2<Gm<G1.Additionally, the rubber hardness of the rim cushion rubber 17 is 70.Additionally, the outer side reinforcing rubber 19 is made of thematerial same as that of the rim cushion rubber 17 and integrated intothe rim cushion rubber 17. The tire cross-sectional height SH is 112 mm,and the length T1 of the perpendicular line drawn from the end portionof the turned back portion 132 of the carcass layer 13 to the outersurface of the tire side portion is 7.0 mm.

In the test tire of Conventional Example, in the structure of the testtire of Example 1, the bead cores 11 have the wire arrangement structureillustrated in FIG. 15. In the test tires of Comparative Examples 1 and2, in the configurations of FIGS. 1 and 2, the amount of the insulationrubbers of the bead cores 11 are increased, and the rubber occupancyratio in the closed region X is increased.

As shown from the test results, it is seen that the test tires ofExamples 1 to 18 can improve the durability of the tires while theweights of the tires are reduced.

1. A pneumatic tire, comprising: bead cores formed by annularly and multiply winding one or a plurality of bead wires; a carcass layer formed of a carcass ply of a single layer or a plurality of layers, the carcass layer being turned back so as to wrap the bead cores and extended between the bead cores; a rim cushion rubber disposed along a turned back portion of the carcass layer to constitute a rim fitting surface of a bead portion; the turned back portion of the carcass layer contacting a body portion of the carcass layer in a cross-sectional view in a tire meridian direction to form a closed region surrounding the bead cores; a rubber occupancy ratio in the closed region being in a range of 15% or less; the bead cores having a predetermined wire arrangement structure formed by arranging wire cross sections of the bead wires in the cross-sectional view in the tire meridian direction; a tangential line L1 and a contact point C2 being defined, the tangential line L1 contacting an innermost layer in a tire radial direction and the wire cross sections innermost and outermost in a tire lateral direction in the wire arrangement structure from the rim fitting surface side, the contact point C2 of the tangent line L1 being on the wire cross section outermost in the tire lateral direction; a gauge Wh in the tire lateral direction from the contact point C2 to the rim fitting surface and an outer diameter φ of the bead wire having a relationship 2.0≤Wh/φ≤15.0; and a radial height H2 of a contact portion between the body portion and the turned back portion of the carcass layer having a relationship 0.80≤H2/H1≤3.00 to a radial height H1 of the bead cores.
 2. The pneumatic tire according to claim 1, wherein a layer in which a number of arrangements of the wire cross sections is a maximum in the wire arrangement structure is defined as a maximum arrangement layer, a number of layers of the wire cross sections outward in the tire radial direction with respect to the maximum arrangement layer is greater than a number of layers of the wire cross sections inward in the tire radial direction with respect to the maximum arrangement layer, and a number of arrangements of the wire cross sections in each layer outward in the tire radial direction with respect to the maximum arrangement layer monotonically decreases outward in the tire radial direction from the maximum arrangement layer.
 3. The pneumatic tire according to claim 1, wherein an arrangement angle θ2 of the wire cross sections at a corner portion inward in the tire radial direction and outward in the tire lateral direction of the wire arrangement structure is in a range 80 degrees≤θ2.
 4. The pneumatic tire according to claim 1, wherein an arrangement angle θ2 of the wire cross sections at a corner portion inward in the tire radial direction and outward in the tire lateral direction of the wire arrangement structure is in a range 100 degrees≤θ2≤150 degrees.
 5. The pneumatic tire according to claim 1, wherein an actual length La2 of a contact portion between the body portion and the turned back portion of the carcass layer has a relationship 0.30≤La2/La1≤2.00 with respect to a circumferential length La1 of the closed region.
 6. The pneumatic tire according to claim 1, comprising an outer side reinforcing rubber that has a rubber hardness higher than a rubber hardness of the rim cushion rubber, the outer side reinforcing rubber being disposed between the turned back portion of the carcass layer and the rim cushion rubber.
 7. The pneumatic tire according to claim 6, wherein a difference ΔHs_RC between the rubber hardness of the rim cushion rubber and the rubber hardness of the outer side reinforcing rubber is three or greater.
 8. The pneumatic tire according to claim 7, wherein when a tire nominal width W (mm), a tire nominal inner diameter I (inch), and a total cross-sectional area B (mm²) of the bead wires in the bead cores are defined, a value K defined by Equation (1) is in a range 0.17≤K; $\begin{matrix} {K = {\frac{W^{\frac{4}{3}} \times I^{\frac{2}{3}}}{100 \times B^{2}}.}} & {{Equation}\mspace{14mu} (1)} \end{matrix}$
 9. The pneumatic tire according to claim 6, wherein a radial height H3 from a measurement point of a tire inner diameter RD to an end portion outward of the outer side reinforcing rubber in the tire radial direction and a tire cross-sectional height SH have a relationship 0.10≤H3/SH≤0.60.
 10. The pneumatic tire according to claim 6, wherein the outer side reinforcing rubber covers an end portion of the turned back portion of the carcass layer from outward in the tire lateral direction.
 11. The pneumatic tire according to claim 6, wherein a radial height H4 from an end portion of the turned back portion of the carcass layer to an end portion outward of the outer side reinforcing rubber in a tire radial direction has a relationship 0.30≤H4/H2 to a radial height H2 of a contact portion between the body portion and the turned back portion of the carcass layer.
 12. The pneumatic tire according to claim 6, wherein a length T1 of a perpendicular line drawn from an end portion of the turned back portion of the carcass layer to an outer surface of a tire side portion and a thickness T2 of the outer side reinforcing rubber on the perpendicular line have a relationship 0.10≤T2/T1≤0.90.
 13. The pneumatic tire according to claim 1, wherein a height Hc2 from the tangent line L1 to a maximum width position of the bead cores and a maximum height Hc1 of the bead cores have a relationship 1.10≤(Hc1−Hc2)/Hc2≤2.80.
 14. The pneumatic tire according to claim 2, wherein an arrangement angle θ2 of the wire cross sections at a corner portion inward in the tire radial direction and outward in the tire lateral direction of the wire arrangement structure is in a range 80 degrees≤θ2.
 15. The pneumatic tire according to claim 14, wherein an arrangement angle θ2 of the wire cross sections at a corner portion inward in the tire radial direction and outward in the tire lateral direction of the wire arrangement structure is in a range 100 degrees≤θ2≤150 degrees.
 16. The pneumatic tire according to claim 15, wherein an actual length La2 of a contact portion between the body portion and the turned back portion of the carcass layer has a relationship 0.30≤La2/La1≤2.00 with respect to a circumferential length La1 of the closed region.
 17. The pneumatic tire according to claim 16, comprising an outer side reinforcing rubber that has a rubber hardness higher than a rubber hardness of the rim cushion rubber, the outer side reinforcing rubber being disposed between the turned back portion of the carcass layer and the rim cushion rubber.
 18. The pneumatic tire according to claim 17, wherein a difference ΔHs_RC between the rubber hardness of the rim cushion rubber and the rubber hardness of the outer side reinforcing rubber is three or greater.
 19. The pneumatic tire according to claim 18, wherein when a tire nominal width W (mm), a tire nominal inner diameter I (inch), and a total cross-sectional area B (mm²) of the bead wires in the bead cores are defined, a value K defined by Equation (1) is in a range 0.17≤K; $\begin{matrix} {K = {\frac{W^{\frac{4}{3}} \times I^{\frac{2}{3}}}{100 \times B^{2}}.}} & {{Equation}\mspace{14mu} (1)} \end{matrix}$
 20. The pneumatic tire according to claim 19, wherein a radial height H3 from a measurement point of a tire inner diameter RD to an end portion outward of the outer side reinforcing rubber in the tire radial direction and a tire cross-sectional height SH have a relationship 0.10≤H3/SH≤0.60. 